Recursive example

[CodeGeek20]

This was given as an example of recursivity. It prints 123456789987654321.

#include <stdio.h>

void printnum ( int begin )
{
    printf( "%d", begin );
    if ( begin < 9 )         /* The base case is when begin is no longer */
    {                           /* less than 9 */
        printnum ( begin + 1 );
    }
    /* display begin again after we've already printed everything from 1 to 9
     * and from 9 to begin + 1 */
    printf( "%d", begin );
}

int main() {
    printnum(1);
}

Now, I can see this code printing 1234567899, but whence does it count back down? I don't see where the code goes back and counts down.

And, I know this has nothing to do with that, but it's easier than two threads. Is it possible to write a program that will open another progam? Such as, a program that will accept integers to select from a menu of programs, like notepad = 1, and then run that program's executable, and close itself?

[King Mir]

Now, I can see this code printing 1234567899, but whence does it count back down? I don't see where the code goes back and counts down.

The easiest way to see what is going on is to run your program through a debugger.

What's happening is the call to printnum(9) is called from printnum(8). So when it returns, it returns back to printnum(8), which continues to execute it's last line, before returning to printnum(7). This goes on untill printnum(1), which returns to main, and ends the program.

And, I know this has nothing to do with that, but it's easier than two threads. Is it possible to write a program that will open another progam? Such as, a program that will accept integers to select from a menu of programs, like notepad = 1, and then run that program's executable, and close itself?

Yes, but it'd be platform specific.

[NeonBlack]

Also, it's not very safe. If someone moves or renames notepad, or worse, replaces it with another executable, your program breaks.
Why do you want to do that? If you want to make a task launcher, fine, but otherwise there is probably a better way.